Historically, various types of nonwoven fibrous structures have been utilized as disposable substrates. The various types of nonwovens used may differ in visual and tactile properties, usually due to the particular production processes used in their manufacture. In all cases, however, consumers of disposable substrates suitable for use as wipes, such as baby wipes, demand strength, thickness, flexibility, texture and softness in addition to other functional attributes such as cleaning ability. Strength, thickness and flexibility can be correlated to certain measurable physical parameters, but perceived softness and texture are often more subjective in nature, and consumers often react to visual and tactile properties in their assessment of wipes. Optimizing all the desirable properties is often not possible.
For example, often a balance of properties results in less than desirable softness or strength levels. Wipes used as baby wipes, for example, should be strong enough when wet to maintain integrity in use, but soft enough to give a pleasing and comfortable tactile sensation to the user(s). They should have fluid retention properties such that they remain wet during storage, and sufficient thickness, porosity, and texture to be effective in cleaning the soiled skin of a user. In addition, sufficient thickness and texture should be retained when wet.
Strength in a nonwoven fibrous structure can be generated by a variety of known methods. If thermoplastic fibers are used, strength can be imparted by melting, either by through-air bonding or by hot roll calendaring. Adhesive bonding is also commonly used to bind fibers to increase the strength of the nonwoven. However, these processes, while increasing the strength of the nonwoven, generally detract from other desirable properties, such as softness and flexibility. Hydroentangling a fibrous structure may generate nonwovens with high softness and flexibility but may reduce the strength of the material. Such a reduction in strength is undesirable for many applications of nonwoven fibrous structures, such as in a wipe application. Due to the nature of cleansing tasks for which wipes are used, consumers prefer a wipe that has a high amount of apparent bulk and strength associated with it. To increase the basis weight of the starting material, such that after hydroentangling the material retains sufficient strength to be used as a baby wipe, would be prohibitively expensive.
The strength, thickness, flexibility and perceived softness may also be affected by any hydro-molding (also known as hydro-embossing, hydraulic needle-punching, etc.) of the nonwoven fibrous structure during manufacture. Hydro-molding is a known means of introducing texture and/or design to the nonwoven structures. As noted above, substrate texture may provide product differentiation, strength, softness and cleaning efficacy. Various images and graphics may be hydro-molded onto the nonwoven fibrous structure. The images and graphics may be a single image or graphic, a group of images or graphics, a repeating pattern of images or graphics, a continuous image or graphic and combinations thereof. It has been discovered, however, that the hydro-molding of images or graphics onto the nonwoven fibrous structure may detract from the desired strength of the fibrous structure.
During manufacture of the fibrous structure, the fibers generally orient in the Machine Direction when laid on a forming member. Such fiber-orientation is common to various formation technologies such as, but not limited to, carding, air-laying, spunbonding, etc. The fibrous web may then be conveyed over a molding member, such as a drum, belt, etc. that may comprise a molding pattern of raised areas, lowered areas, or combinations thereof interspersed thereon. The pattern may be used to mold the image, graphic or texture onto the fibrous web thereby creating a molded fibrous structure. The resulting image, graphic, or texture on the fibrous structure may be a molded element of the fibrous structure.
In a typical manufacturing process where the molding pattern is meant to consist of discrete or disjoined elements of a repeating pattern, each element would be represented on the molding member as a complementary discrete element. Additionally, where the molding pattern is meant to incorporate at least one continuous element extending across the width or along the length of the non-woven, the molding member must be constructed so that the lowered areas of the molding pattern are continuous along either the length or the width of the fibrous structure.
In a manufacturing process for textures incorporating a continuous molding pattern, the continuous pattern may optionally be oriented in either the Machine Direction (i.e. parallel to the dominant fiber-orientation direction) or in the Cross Direction (i.e. perpendicular to the dominant fiber-orientation). It has been found that hydro-molding a continuous molding pattern onto a fibrous structure, in which the lowered areas on the molding member are oriented in the Machine Direction, may produce a molded element on a fibrous structure that is weak in strength because there are fewer fibers oriented in the Cross Direction to provide continuity and, as such, strength across the molded element. A lack of strength can result in a molded fibrous structure that may easily rip and fall apart.
Thus, there is a need to maintain the strength of a fibrous structure incorporating a continuous molded element. There remains a need to provide a substrate from a molded fibrous structure.